Currently, an existing example of antenna device is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2016-100609). Patent Document 1 discloses an antenna device that includes an antenna coil, a resin-made antenna case having a recess for accommodating the antenna coil, and a filler for sealing the antenna coil accommodated in the recess.
For example, a vehicle-mounted antenna device used for a smart keyless system or the like is typically mounted on a metal plate of a vehicle body by using a fastening member, such as a screw or a clip. In this case, if the antenna device is mounted where the device is stepped on, a load exceeding 100 kg, for example, may be applied to the antenna device.
To address this concern, the known antenna device has a thickness of the antenna case that is increased so as to improve the load bearing capability. However, increasing the thickness of the antenna case requires an increased amount of resin, which leads to an increase in weight and manufacturing cost of the antenna case.